Resonant DC to DC converters are considered by many to be attractive power conversion solutions for the many benefits they can provide. Following a resonant tank with transformers provides galvanic isolation which is important for level conversion as well as for safety. In certain applications, such as thin film solar panels, galvanic isolation is required for proper operation. Resonant converters also have inherent properties, such as soft switching of the semiconductor switches, which lead to high efficiency and low noise.
A commonly used type of resonant converter is known as the LLC resonant converter, named for the two inductors and one capacitor used to form its resonant tank. The LLC resonant converter has gained popularity due to its ability to achieve high efficiency. However, drawbacks of this type of converter include high AC currents in the output capacitors resulting in higher than desired power losses as well as the large volume or size taken up by the output filter components.
Combining or paralleling multiple LLC converters and interleaving their outputs with appropriate pulse width modulation (PWM) can reduce output ripple current and help reduce the volume required for the output filter capacitor. However due to voluntary and regulatory requirements, further improvements in efficiency and size are still desirable and may be required in certain applications. Thus, there is a need for improved resonant DC to DC converter topologies that can deliver better efficiency and low noise from smaller packages.
Accordingly, it would be desirable to provide a DC-DC converter topology that addresses at least some of the problems identified above.